While volatile memories, such as dynamic random access memories (DRAMs) provide a method to store information, many applications today make use of non-volatile memories devices that will retain information even when power is removed.
Presently, virtually all nonvolatile memories are some type of read only memories (ROMs). One group of nonvolatile memories consists of ROMs in which data is entered during manufacturing that cannot be subsequently altered. These devices are known as masked ROMS. Another group of nonvolatile memories consists of memories whose data can be entered by the user. This group is known as a programmable ROM or PROM in which data can only be entered once.
There is one common element among the programmable structures that reside in PROMS, and a RAM having programmable options available and that is the need for an internal programmable element.
In recent years, programmable antifuse elements have been developed for use in various integrated circuit applications (such as the antifuse element disclosed in U.S. Pat. No. 4,899,205, herein incorporated by reference). In order to be able for an antifuse element to be incorporated into state-of-the-art IC fabrication, a low, voltage, low current antifuse element is essential. In addition, a low resistive post programming behavior is important in order to distinguish between "on" and "off" states (or "programmed" and "unprogrammed" states).